This application claims the benefit of the Korean Application No. P2001-87849 filed on Dec. 29, 2001, which is hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly, to a liquid crystal display device and fabricating method thereof to prevent the generation of afterimage and flickers by increasing a capacitance of a storage capacitor.
2. Discussion of the Related Art
A liquid crystal display device has characteristics of low-voltage driving, low power consumption, full-color realization, lightness and compact size, and the like, thereby becoming applicable to TV, aircraft monitors, PDA and mobile phones, as well as calculators, watches, notebook computers, and personal computers.
Generally, a liquid crystal display device includes a thin film transistor substrate having thin film transistors and pixel electrodes in pixel areas defined by gate and data lines, respectively, a color filter substrate having a color filter layer and a common electrode, and a liquid crystal layer inserted between the two substrates.
In order to drive such a liquid crystal display device, a thin film transistor switches an electrical signal and liquid crystals realize an image in accordance with the signal. Thus, in order to realize a stable image when a liquid crystal display device is driven, the liquid crystals should also be driven while the thin film transistor is turned off. To achieve this, while the thin film transistor is turned on, electric charges are accumulated on a storage capacitor. However, if a capacitance of the storage capacitor charged with the electric charges is not sufficient, afterimage and flickers occur on a screen.
A structure of a liquid crystal display device and a fabricating method thereof according to a related art device are explained by referring to the attached drawings as follows.
Referring to FIG. 1, a unit cell of a liquid crystal display device according to a related art device includes gate and data lines 102a and 150 crossing each other on a substrate (not shown)and a pixel electrode 108 formed in a pixel area defined by the gate and data lines 102a and 150.
Moreover, the unit cell of the liquid crystal display device further includes a drain electrode 106b connected to the pixel electrode 108 through a contact hole 107a and a capacitor electrode 106c over the gate line 102a. In this case, the capacitor electrode 106c is connected to the pixel electrode 108 through the other contact hole 107b. 
Referring to FIG. 2A, in order to form a unit cell of a liquid crystal display device having the above-explained structure, first of all, a gate electrode 102 and a gate line 102a are formed on a substrate 100.
Subsequently, a gate insulating layer 103 is formed on the gate electrode 102 and gate line 102a. An active layer 104 and an ohmic contact layer 105 are formed on the gate insulating layer 103 overlapped with the gate electrode 102. In this case, a thickness of the gate insulating layer 103 is even all over the gate electrode 102, gate line 102a, and substrate 100.
Referring to FIG. 2B, source and drain electrodes 106a and 106b are formed on the ohmic contact layer 105. A capacitor electrode 106c is simultaneously formed with the same material forming the source and drain electrodes 106a and 106b on the gate insulating layer 103 overlapped with the gate line 102a. 
In this case, the capacitor electrode 106c, gate line 102a, and the gate insulating layer 103 between the capacitor electrode 106c and gate line 102a constitute a storage capacitor. Hence, the thickness of the gate insulating layer 103 becomes an important variable for capacitance of the storage capacitor. Particularly, if the gate insulating layer 103 is thick, the capacitance of the storage capacitor is reduced so as to generate afterimage and flickers on a screen. Yet, if the gate insulating layer 103 is formed thin to increase the capacitance of the storage capacitor, a parasitic capacitance is generated from the thin film transistor including the gate electrode 102, source and drain electrodes 106a and 106b, and the gate insulating layer 103 between them. Hence, the thin film transistor becomes unstable.
Referring to FIG. 2C, a passivation layer 107 having contact holes 107a and 107b is formed on an entire surface of the structure.
Referring to FIG. 2D, a pixel electrode 108 is formed on the passivation layer 107 using ITO(indium tin oxide).
In this case, the drain electrode 106b and pixel electrode 108 are electrically connected to each other through the contact hole 107a, and the capacitor electrode 106c and pixel electrode 108 are electrically connected to each other through the other contact hole(xe2x80x98107bxe2x80x99 in FIG. 1).
Unfortunately, the liquid crystal according to the related art has the following problem or disadvantage.
If the gate insulating layer is thick, the capacitance of the storage capacitor is decreased so as to generate the afterimage and flickers on the screen. On the contrary, if the gate insulating layer is formed thin so as to increase the capacitance of the storage capacitor, performance of the thin film transistor becomes unstable.
Accordingly, the present invention is directed to a liquid crystal display device and fabricating method thereof that substantially obviates one or more problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide a liquid crystal display device and fabricating method thereof to increase a capacitance of a storage capacitor as well as stabilize performance of a thin film transistor.
Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objectives and other advantages of the invention may be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these objects and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, a liquid crystal display device according to the present invention includes a gate electrode and a gate line on a substrate, a gate insulating layer covering the gate electrode, gate line, and substrate, an active layer formed over the gate electrode so as to leave the gate insulating layer therebetween, source and drain electrodes on the active layer, a capacitor electrode formed over the gate line so as to leave the gate insulating layer therebetween, a passivation layer on the drain and capacitor electrodes so as to have contact holes, and a pixel electrode on the passivation layer.
Preferably, a thickness of the gate insulating layer under the active layer is twice as thick than the thickness of the insulating layer in another area.
More preferably, the gate insulating layer under the active layer is about 4,000 xc3x85 thick.
More preferably, the gate insulating layer in another area is about 2,000 xc3x85 thick.
Preferably, the liquid crystal display device further includes an ohmic contact layer between the source/drain electrodes and the active layer.
In a further aspect of the present invention, a method of fabricating a liquid crystal display device includes the steps of forming a gate electrode and a gate line on a substrate, depositing a gate insulating layer on the gate electrode, gate line, and the substrate, forming an active layer on the gate insulating layer over the gate electrode, etching the gate insulating layer to a predetermined thickness in all other areas except an area under the active layer, and forming source and drain electrodes on the active area and a capacitor electrode on the gate insulating layer over the gate line.
Preferably, the gate insulating layer is deposited about 4,000 xc3x85 thick.
Preferably, the step of forming the active layer includes the steps of depositing a polysilicon layer on an entire surface of the gate insulating layer, forming a photoresist pattern on the polysilicon layer, and etching the polysilicon layer selectively using the photoresist pattern as a mask.
More preferably, the polysilicon is etched by a dry etch technique.
Preferably, the gate insulating layer in the rest of the areas except the area under the active layer is etched by a dry etch technique.
Preferably, the gate insulating layer in the rest of the areas except the area under the active layer is etched so as to be 2,000 xc3x85 thick.
Preferably, the method further includes the step of forming an ohmic contact layer on the active layer.
Preferably, the method further includes the steps of forming a passivation layer on the source, drain, and capacitor electrodes and forming a pixel electrode on the passivation layer.
More preferably, a first contact hole for connecting the drain and pixel electrodes to each other and a second contact hole for connecting the capacitor and pixel electrodes to each other are formed in the passivation layer.
It is to be understood that both the foregoing general description and the following detailed description of the present invention are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.